1. Field of the Invention
This invention is directed to a system for the use of multiple liquid blasting guns; to controls for liquid blasting systems; and particularly to dump control valves for water blasting systems.
2. Description of the Prior Art
Water blasting systems are used to produce a high pressure stream of water or water and abrasive particles to clean parts; to clean surfaces; and to blast away scale, paint, rust or contaminants. Such systems have applications in oil refineries, chemical plants, oil field operations, offshore operations and marine industries. These systems utilize pumps which produce pressures up to 50,000 p.s.i.
A high pressure liquid stream is fed to nozzle assemblies or to individually-held guns such as that disclosed in U.S. Pat. Nos. 3,799,440 and 3,802,628. Generally such guns are designed so that upon the pulling of a trigger mechanism, high pressure water flows out of a high pressure nozzle in the gun end. Upon releasing of the trigger, water is directed to a dump port in the gun and flows out of the dump port under very low pressure. Often a plurality of such guns is connected to a single power source. When multiple guns are so powered, often an individual operator encounters numerous occasions when he must shut down his gun and then start it up again. Also with such multiply-connected guns, when the pressure is reduced at a shut-down gun, the output pressure of the power system for the remaining guns may be reduced below an operable level.
Two prior art methods for operating multiple guns from a single power source are illustrated in FIGS. 1 and 2. In the method of FIG. 1, a pump P supplies fluid under pressure to nozzles 1, 2, 3, and 4 via hoses a, b, c, d, e, f, g. All the nozzles are the same size. Control valves I and II are operable to affect the flow from hose d to f and hose e to g, respectively. When both control valves I and II are closed, the pressure at the nozzles 2 and 4 is one-half the pump pressure; e.g. if valve I is closed, then only half the pressure delivered by pump P is available to nozzle 2. When valve I is "closed" flow is possible between hose d and hose f. Valves I and II are referred to as "dump style control valves" which they "dump" relieve the pressure in hoses d, e, f, and g. An "open" valve is one permitting flow; e.g. when valves I and II are open, flow is possible from hoses d and e to the atmosphere. The pressure drop across nozzles 1 and 3 respectively is full pump pressure. Therefore the operators of nozzles 2 and 4 are not affected when either valve I or II is open or closed. With the method of FIG. 1, only half the pump pressure is available at the nozzles. Also, when one operator dumps his gun (i.e. releases the trigger causing water to cease flowing out of the gun's high pressure nozzle and to begin flowing out of the gun's dump port), there is no pressure at the gun's nozzle and valve I opens to the atmosphere. This reduction is pressure causes water flowing through lines c and e to also flow back around the circuit and out of valve I, i.e., this water also seeks the path of least resistance and rather than going out the high pressure nozzle 4 it goes out the valve I. Of course, this means that the operator of gun with nozzle 4 experiences an unexpected pressure loss which could be dangerous if the operator is leaning into the gun to counteract its tendency to push backward or whip around during operation.
FIG. 2 illustrates another prior art system for the use of multiple guns with a single power source. In this method the flow to each gun A and B is governed by pneumatically-powered two-position valves, III and IV; e.g. in a first position of valve III flow is from line a, through line c, and then through line h. Safety valves C and D allow pressure at nozzles A and B to be reduced to atmospheric pressure of valves III and IV fail in their second positions ("Pos. 2"). While in their first positions ("Pos. 1"), valves III and IV allow flow to nozzles E and F such that the pump pressure at P remains the same. This method maintains constant pressure on the pump and allows each gun operator to blast at full pump pressure. However, with this method a supply of compressed air is required to operate the pneumatically powered valves III and IV. Also this method requires signal lines from dump valves C and D to control valves III and IV (in FIG. 2, these lines are lines j and k).
There has long been a need for a relatively inexpensive system which does not require compressed air or signal lines and which is safe and efficient.